Rubber elastic engine mounts or supports with hydraulic damping

ABSTRACT

Elastic rubber engine mounts with hydraulic damping are provided, especially for engine suspensions in motor vehicles. The mounts comprise two separated liquid-filled chambers, defined in part by elastic rubber-like peripheral walls adheringly connected with end walls and with a centrally disposed supporting element for connection to an engine supporting frame. The liquid chambers are separated by an elastic rubber-like partition connected with the supporting element, and flow connection between the two chambers is provided by perforations or choke openings in the partition. The rigid end walls of the two chambers are ridgidly interconnected. Arrangements are provided for minimizing or avoiding hydraulic damping of oscillations of low amplitude and high frequency, while providing hydraulic damping for oscillations of large amplitude and low frequency. This is achieved by limited compensation of volume changes in the chambers, through either axially reciprocable annular members disposed in the partition and axially movable relative to the support element, or by flexible wall parts in the rigid end walls. The flexible wall parts may be in the form of diaphragms, and the diaphragms may advantageously be of foamed material. Hydraulic damping thus occurs only upon oscillations of predetermined amplitude and frequency.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of our earlier applicationSer. No. 791,309, filed Apr. 27, 1977.

FIELD OF THE INVENTION

This invention relates to liquid-filled rubber or elastic engine mountsor bearings with hydraulic damping, especially for supporting ormounting engines in motor vehicles so as to vibrationally insulate thevehicle frame from the engine. More particularly, this invention relatesto such engine mounts of the type disclosed in our copending applicationSer. No. 791,309, filed Apr. 27, 1977. The present application is acontinuation-in-part application of our said parent application, and thedisclosure of said parent application is incorporated herein byreference. The engine mounts disclosed and claimed in the instantapplication present improvements and/or variations of the mountsdisclosed in our said parent application.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention of this application is directed to the problem ofproviding such an engine mount with simple means which meet therequirement that oscillations of the engine casing be hydraulicallydamped by the engine mount when such oscillations are of low frequencyand relatively great amplitude, and that high frequency oscillationswith relatively small amplitudes of, for example, 0.1 mm remainhydraulically undamped as far as possible, whereby the vehicle frame orrelated engine supporting elements will not be loaded with hydraulicdamping stresses.

Engine mounts of the type to which the instant invention relatesgenerally comprise a first metallic end wall for connection to an enginecasing, a second metallic end wall spaced axially from the first wall, ametallic supporting element for connection to an engine supportingframe, a first elastic rubber-like peripheral wall adheringly connectedwith the first end wall and with the supporting element, a partitionconnected with the supporting element so as to define with the first endwall and the first peripheral wall a liquid-filled main chamber ofvariable volume on one side of the partition, a second elasticrubber-like peripheral wall adheringly connected with the second endwall and with the supporting element so as to define an auxiliaryliquid-filled chamber of variable volume on the other side of thepartition, means such as perforations or choke openings defining a flowconnection between the main and auxiliary chambers, and means rigidlyconnecting the first and second end walls together for joint movementrelative to the supporting element.

In one approach taken by the instant invention, there is disposed in thepartition an annular member forming choke openings or connectionsbetween the main chamber and the auxiliary chamber, the annular memberbeing disposed so as to be axially movable with reference to thepartition and being limited in its stroke in the middle of thepartition. Preferably the stroke of the annular member through themiddle of the partition is such that the stroke volume of the annularmember (the axially facing surface area of the annular member multipliedby the stroke distance) corresponds to the displacement volume of theliquid filled chambers with a total oscillation path of the engine mountof up to 0.2 to 0.3 mm. In this way, the engine oscillations up to thisrange cause substantially no liquid exchange between the chambers, butrather only a shifting or stroke of the annular member, wherebyadvantageously only a very small shifting force results, actingindirectly via the rubber-elastic peripheral walls on the metallicsupporting element, because the mass of the annular member can be verysmall. With increasing oscillation paths, there is a gradual exchange ofliquid between the main chamber and the auxiliary chamber that exertsdamping forces, until with oscillation paths of, for example, 5 mm ormore, strong damping forces are established by the flow resistance ofthe choke openings.

Advantageously a plate-like annular member is surrounded by an inwardlyopening groove in the partition, whereby the groove flanks form impactsurfaces, or alternatively the annular member is provided with U-shapedoutwardly directed flanges that extend to impact surfaces on thepartition. Here the impact surfaces of the partition and of the annularmember may simply constitute tight contact surfaces in a stroke-limitedstate. If the annular member in non-stroke-limit positions presents freeannular gaps with respect to the partition, the annular member canoscillate undamped between the impact surfaces of the annular member andthe partition, and also the possible exchange of volume between thechambers can additionally suppress or ameliorate the occurrence ofhydraulic damping forces at small amplitudes. The choke openings can beprovided directly in a plate-like annular member, or in an intermediatewall of the annular member. Advantageously the annular member has onlyone choke opening which determines flow resistance with its fullcross-section, or forms an annular cross-section that determines flowresistance with a bolt that connects the end walls. The intermediatewall of the annular member that is provided with a choke opening, or thewhole annular member, can be made of a rubber-elastic material, wherebythe choke opening may present a lip-like edge with a flow profile ofspecial configuration turned toward the opening, which edge portion canbe deformed by the flow forces to effect an enlargement or a reductionof the flow cross-section and a change of the throughput coefficient.Thus the flow resistance of the choke opening can be influenced orvaried as desired, with increasing liquid exchange between the twochambers.

The annular member can be joined to the partition by a thin elasticflange, whereby also the deformation strength of the flange can limitthe stroke of the annular member.

If an annular member penetrated by a connecting bolt presents a freeannular gap and/or at least a resilient lip of elastic material in theregion of the choke opening, there is achieved the advantage of readytransverse mobility of the walls that are rigidly joined by theconnecting bolt, with reference to a partition that has littleresilience.

In another aspect of the instant invention, the previously mentionedproblem is solved by providing in one or both end walls openings orperforations that are covered by resilient wall parts which pose adecreasing resistance to a change of the fluid pressure in theappurtenant chamber, that is, the main chamber or the auxiliary chamber.Otherwise stated, these resilient wall parts are initially flexible soas to compensate for any volume change in the chamber, and hence resista change of fluid pressure in the chamber, but thereafter the resilientwall parts reach the limit of their resilience so as not to compensatefurther or to the same degree to volume changes of the chamber, suchthat the fluid pressure in the chamber will rise rapidly. Thus thevolume changes in the chambers per unit of time, at low amplitudes andhigh frequencies, are compensated by a corresponding movement of theresilient wall face parts without the need for any liquid exchange worthmentioning to occur through the choke opening, whereas at largeamplitudes and low frequencies the volume changes or liquid volumesforced per unit of time, which volumes may be of the same totalmagnitude, will only in small part be taken up by the resilient wallparts, and the essential portion of the liquid must flow exclusivelythrough the choke opening as soon as the resilient wall parts haverespectively reached a limit of their yielding.

By the measures provided by this aspect of the invention, advantageouslyat small amplitudes and high frequencies the pressure building up in thechambers can be kept low by an appropriate dimensioning andconfiguration of the resilient end wall parts, and hydraulic dampingwill therefore be slight or insignificant, whereas at large amplitudeswith low frequencies the pressure that is building up can be keptrelatively high by suitable dimensioning and configuration of the chokeopening, and hence hydraulic damping to the required degree will beattained.

In the inoperative state of an engine mount in accordance with thesecond aspect that is ready for operation, the chambers advantageouslyare at a pressure that is at or only slightly above or below atmosphericpressure. Then, if one considers approach of the end wall on the engineside to the supporting element to be the compression stage, and retreatof the said end wall from the supporting element to be the suctionstage, with large volumes, evoked by large amplitudes in the compressionstage only in the main chamber and in the auxiliary chamber only in thesuction stage, pressure differences will occur that are determined bythe actual flow resistance of the choke opening, the differences movingthe resilient wall parts outwardly, while the auxiliary chamber in thecompression stage and the main chamber in the suction stage will retainessentially the initial pressure. Consequently in both chambers therewill only be slight pressure differences that tend to move the resilientwall parts inwardly.

Advantageously the resilient wall parts are made as diaphragms that aretightly joined with the edges of the openings or perforations in the endwalls. The resilient wall parts can be made especially simply if aperforated wall face and rubber elastic diaphragms are adheringly joinedat the edges of the perforations, forming a vulcanized rubber metallicpart. The diaphragms can be made so that they are substantially flat inthe dynamic middle position of an operational engine mount. As soon as adiaphragm of suitable dimensions and configuration is bulged morestrongly outwardly or inwardly from the basic position, the deformationstrength or resistance thereof increases progressively, and, with largeamplitudes, it can build up the desired pressure in the chambers. If thedeformation strength of a diaphragm or other resilient wall part isinadequate for this purpose, simple mechanical ancillary means canreenforce the resistance of the resilient wall part with respect to theoccurring pressure difference, e.g., a plate connected with the end wallcan constitute an impact surface which limits the give of the diaphragmor similar part, after a predetermined stroke. The resilient wall partsmay also be made as diaphragm parts applied to the inner side of aperforated wall face, whereby advantageously a diaphragm that covers thewhole inside may lie freely on the wall face or be adheringly joinedthereto. Material for diaphragms of this kind may also be a foamedmaterial, especially polyurethane, made up of individual bubbles,whereby the resilience of the diaphragm with reference to theperforations or openings and the intrinsic resilience of the foamedmaterial are summed, and acting together in case of high frequencyoscillations and low amplitudes they compensate the volumes forced inthe chambers, or the volume changes of the chambers. If such a foameddiaphragm is provided on the liquid side with a thin metallic or plasticfoil, gas or liquid exchange between the individual bubbles and theappurtenant chamber can be reliably avoided, and it can even beprevented that a diaphragm without a foil will be punched through theperforations if the pressure in the chamber becomes increasingly high.

In general it is advantageous to equip both end walls of the enginemount with resilient wall parts in order to be able to compensate forcedvolume changes at low amplitudes and high frequency oscillation. If theelastic peripheral wall on the engine side essentially determines theelastic bearing capacity of the engine mount, and the peripheral wallaway from the engine is so resilient that by corresponding deformationit can compensate the forced volumes in case of small amplitudes andhigh frequencies, it suffices to provide resilient wall parts only forthe end wall toward the engine. There may be other reasons also forequipping only one end wall with resilient wall parts according to theinvention, particularly if other supplementary measures of some otherkind are provided for the engine mount to suppress hydraulic dampingwith high frequency oscillations and low amplitudes. It should beobserved that quite generally other measures which are frequency oramplitude dependent may be combined with the invention to reinforce theeffect described here, to influence the damping in the desired way, forother characteristic frequency/amplitude ranges, e.g., to reenforce themor to reduce them.

Other features, advantages and aspects of the invention will becomeapparent to those skilled in the art from the ensuing description ofpreferred embodiments, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in sectional elevation an engine mount in keeping with thefirst discussed aspect of the invention, in a static setting with aplate-like annular member penetrated by a connecting bolt.

FIG. 2 shows an engine mount similar to FIG. 1, but with a differentkind of annular member, having faces rigidly connected by an arcuatemember.

FIG. 3 is a cut-away view of a mount similar to FIG. 1, having a rubberelastic annular member connected with the partition.

FIG. 4 shows an engine mount in accordance with the second discussedaspect of the invention, in section, with an end wall on the engine sidethat presents four elastic diaphragms adheringly joined to the edges offour perforations or openings, and an end wall turned away from theengine, on the inside of which there is a diaphragm of foamed material.

FIG. 5 is a plan view of the end wall of the mount of FIG. 4, the endwall being the upper end wall on the engine side as viewed in FIG. 4.

Referring to FIG. 1 elastic peripheral wall 1 on the engine side isadheringly joined at its outer periphery with a metallic jacket 2, andat its inner periphery with a conical jacket 4. Jacket 2 is fixed bymeans of a flange 2' to an end wall 7 on the engine side. Conical jacket4 and a flange 15 that is integral therewith form a supporting elementor backup 27 which is bolted by bolts 40 on an engine support frame 41of a vehicle chassis that is not otherwise illustrated. A rubber elasticperipheral wall 8 on the side away from the engine is adheringly joinedat its outer periphery in the region of its major diameter with ametallic jacket 9, and at its outer periphery in a tapered region 8' ofsmaller diameter with the supporting element 27. Jacket 9 is fixed by aflange 9' to an end wall 14 turned away from the engine. A connectingbolt 21, which has a shoulder 18' turned away from the engine and ashoulder 18" on the side toward the engine, is connected by nut 60 withwall 14, and by a plate 61 with wall 7, and thus connects the two endwalls 14 and 7 rigidly with each other. Wall 7 is fixed by means of athreaded extension 24 of bolt 21, and a nut 25, to engine housing orcasing 26. A rubber elastic partition 3 is adheringly joined at itsouter periphery with conical jacket 4 of supporting element 27, and ismade integrally with peripheral wall 8.

Partition 3 has an inwardly opening groove 28 which presents a rubberelastic groove flank 29 on the engine side and a flank 30 facing awayfrom the engine, flank 30 being formed by a plate 31 rigidly anchored inthe partition. Groove 28 encloses a rubber elastic annular member 33which is penetrated by connecting bolt 21 and provided with a partition32. This member 33 is movable in all directions in the illustratedposition, and its axial stroke is limited by groove flanks 29 and 30which act as impact surfaces. With the radially outer surface of groove28, annular member 33 forms a free annular gap 34. Partition 32 withconnecting bolt 21 forms an annular choke opening 35, and in the regionof choke opening 35 it presents a lip-shaped edge 36 with arcuateprofile, whose crest 37 is in the middle of choke opening 35. Edge 36,when annular member 33 is held fixed, is relatively easily deformedtransversely by connecting bolt 21 when contact is made between thesemembers.

A main chamber 19 is limited by peripheral wall 1 and end wall 7, anddivided off by partition 3 and annular member 33 from an auxiliarychamber 20 that is defined by peripheral wall 8 and end wall 14. Mainchamber 19 and auxiliary chamber 20 are filled with a hydraulic fluid,and are connected via choke opening 35. In the illustrated position ofannular member 33, there is another connection of chambers 19 and 20along a flow path via a gap 38 formed by annular member 33 and grooveflank 29, annular gap 34, and gap 39 formed by annular member 33 andgroove flank 30.

The axially facing displacement surface of annular member 33 (e.g. theupper surface as viewed in FIG. 1) multiplied by the summed gap width ofgap 38 and 39 determines a maximum stroke volume (stroke displacementvolume) of annular member 33. With very small oscillation amplitudes ofend walls 7 and 14 with reference axially to support element 27, wherethe volume which tends to move between chambers 19 and 20 does notextend the stroke volume of annular member 33, this member 33 canoscillate back and forth between groove flanks 29 and 30, wherebysubstantially no liquid exchange occurs between chambers 19 and 20, andhence no hydraulic damping of the oscillations of the engine mountoccurs. With oscillations of greater amplitude, with liquid volumetending to move between the chambers that exceeds the stroke volume ofannular member 33, there is an exchange of liquid between chambers 19and 20 through choke opening 35, according to the momentaryflow-conditioned application of annular member 33 on flank 29 or onflank 30. The throughput quantity at choke opening 35 is so much thegreater, the greater the oscillation path remaining after application ofannular member 33 to flank 29 or 30, and between chambers 19 and 20there will be a pressure differential caused by the flow resistance ofchoke opening 35, whereby the throughput velocity with a giventhroughput quantity will depend upon the flow through the cross-sectionof choke opening 35, and the flow coefficient of choke opening 35 isdetermined by the profile of edge 36.

In the illustrated position of partition 32, edge 36 causes anozzle-like intake flow and a nozzle-like discharge flow. When partition32 is bent as a result of a correspondingly great pressure differencebetween chambers 19 and 20, the flow cross-section as well as the flowcoefficient of choke opening 35 will change, since the intake flow willnot remain nozzle-like, but will have an acute angle. This causes apronounced rise in the flow resistance of choke opening 35 withreference to an unvariable profile of edge 36. With a suitableconfiguration of edge 36, it can likewise be arranged to have the flowresistance rise less, particularly if with increased bending of a softpartition 32 the flow cross-section of choke opening 35 can be made muchlarger. The flow behavior of the illustrated device can be affected by asupplementary control function of annular member 33, e.g. by providingperforations in plate 31 which remain open when annular member 33 isapplied to groove flank 30, and which have no effect if annular member33 is applied to groove flank 29. The flow resistance of the device thuscan be made of different magnitudes, depending upon the direction offlow; in the mentioned case, it would be less with emptying of mainchamber 19 into auxiliary chamber 20, than with filling from auxiliarychamber 20.

Referring now to FIG. 2, in the engine mount or bearing according tothis figure a main chamber 119 is defined by a peripheral wall 101 thatis adheringly joined to a backup or support element 127, and an end wallstructure generally designated 107, and divided from an auxiliarychamber 120 by a partition 103 that is adheringly joined to supportelement 127, in conjunction with an annular member 133, the auxiliarychamber 120 being defined by a peripheral wall 108 and an end wall 114.Support element 127 can be conventionally connected with an enginesupporting frame, as in the embodiment of FIG. 1. End walls 107 and 114present outwardly projecting pins 46 and 45, respectively, and areconnected by nuts 47 and 44 with a C-shaped supporting arm 43, such thatthe pins 46 and 45 can be slid laterally into the supporting arm 43.Supporting arm 43 connects end walls 107 and 114 rigidly with eachother, and it can be connected in a conventional manner with the enginehousing or a part of the engine housing.

Annular member 133, which comprises a metallic ring and a rubber elasticpartition 132 adheringly connected therewith, has two outwardly directedU-shaped flanges 48 and 49 which extend over partition 103, with member133 being movable to all sides with reference to partition 103. Theaxial stroke of annular member 133 is limited by faces 129 and 130 ofpartition 103. Partition 132 presents a choke opening 135, in which theedge 52 turned toward main chamber 119 is sharply angular, and the edge51 turned toward auxiliary chamber 120 is rounded, so that choke opening135 has different flow coefficients in the two directions of flow. Thefunction of the engine mount, of course, corresponds to the previouslydescribed function of the engine mount of FIG. 1.

In accordance with the further embodiment illustrated in FIG. 3, arubber elastic annular member 233 with a partition 232 is made as onepiece with a partition 203, and is joined with partition 203 by a thinflange 50. Partition 232 constitutes a choke opening 235, together witha bolt 221 that penetrates annular member 233. Flange 50 offers onlyslight opposition to small axial movements of annular member 233, sothat the function of annular member 233 with small movement is similarto that of annular member 33 of FIG. 1. With larger movements thedeformation strength of flange 50 is substantial, and annular member 233is to be considered to be stroke limited in the sense of the invention.

Referring now to FIGS. 4 and 5, which illustrate an embodiment inkeeping with further aspects of the invention, a rubber elasticperipheral wall 401 on the engine side is adheringly joined at its outerperiphery with a metallic jacket 402 and at its inner periphery to aconical jacket 404. Jacket 402 is fixed to wall face 407 on the engineside by means of a flange 402'. Conical jacket 404 and a flange 415 thatis made as one piece therewith constitute a supporting element or backup427 which is fastened by bolts 450 to an engine support frame 451 of avehicle structure. A rubber elastic peripheral wall 408 on the side awayfrom the engine is adheringly joined at its outer periphery in theregion of its major diameter with a metallic jacket 409, and at itsouter periphery in a tapered region 408' (which has a smaller diameterthan that of jacket 409) with supporting element 427. Jacket 409 isfixed by a flange 409' to end wall 414 relatively away from the engine.A connecting bolt 421 which has a shoulder 418' turned away from theengine and a shoulder 418" on the side toward the engine is connected bynut 460 with end wall 414 and by a plate 461 with end wall 407, therebyconnecting the two end walls rigidly with each other. End wall 407 isfixed by extension 424 of bolt 421 and a nut 425 to engine housing 426.A rubber elastic partition 403 is adheringly joined at its outerperiphery with conical jacket 404, and is provided with a neck 410 onthe side turned relatively away from the engine, which neck ends in acollar 411 reenforced by an angular metal insert 412. A main chamber 419is constituted by peripheral wall 401 and end wall 407, and divided offby partition 403 from an auxiliary chamber 420 which is formed byperipheral wall 408 and end wall 414. Chambers 419 and 420 areinterconnected via an annular gap 431 between collar 411 and bolt 421,which serves as a choke opening.

The engine mount is shown in an inoperative, operation-ready positionwhich at the same time is a dynamic mid-setting of the mount. End wall407 has four openings or perforations 447, or consists, like a wheel, ofa rim 440 and four spokes 441. Each perforation 447 is covered by adiaphragm 442 of rubber elastic material which is adheringly joined toedge 444 of the opening of perforation 447. Spokes 441 are covered onboth sides by rubber elastic material. On the left side of FIG. 4, aspoke 441 is shown in section, while the right side shows a sectionthrough a diaphragm 442. A wall face 462 of plate 461 toward end wall407 constitutes an impact surface that limits an outwardly directedstroke of diaphragm 442 to, for example, a stroke of 1 mm, whereby theappurtenant stroke of wall 407 (which causes a corresponding volumechange in main chamber 419) with reference to support element 427 isless, being for example 0.2 mm. End wall 414 has a plurality of openingsor perforations 448 which, as shown on the left side of FIG. 4, arecovered by a foamed material diaphragm 445 disposed on the inside of endwall 414. The right side of FIG. 4 shows a foamed material diaphragm 446covering end wall 414, the side of the diaphragm turned toward auxiliarychamber 420 being reenforced by a foil 449.

Peripheral wall 401 on the engine side is made stronger than peripheralwall 408 on the side away from the engine, and essentially determinesthe elastic bearing strength of the engine mount or bearing. Peripheralwall 408 is capable of creating a volume balance, because of a somewhatdiaphragm-like construction of the zone that forms a generally flatannular flange 408", if with a specific axial displacement of walls 407and 414 the changes in volume evoked in main chamber 419 and auxiliarychamber 420 differ from one another. In this way it will be preventedthat there may be negative pressure with noise-causing cavitation inchamber 419 or 420.

Thus having described our invention in the manner required by thestatutes, including preferred embodiments thereof, we claim:
 1. Anelastic rubber engine mount with hydraulic damping, especially forengine suspensions in motor vehicles, comprising a first metallic endwall for connection to an engine casing, a second metallic end wallspaced axially from said first wall, a metallic supporting element forconnection to an engine supporting frame, a first elastic rubber-likeperipheral wall adheringly connected with said first end wall and withsaid supporting element, an elastic rubber-like partition connected withsaid supporting element so as to define with said first end wall andsaid first peripheral wall a liquid-filled main chamber of variablevolume on one side of said partition, a second elastic rubber-likeperipheral wall adheringly connected with said second end wall and withsaid supporting element so as to define an auxiliary liquid-filledchamber of variable volume on the other side of said partition, meansrigidly connecting said first and second end walls together for jointmovement relative to said supporting element, an annular member disposedin said partition and formed with a choke opening providing flowconnection between said chambers, said annular member being relativelyfreely axially movable normal to and relative to said partition, suchthat said limited movement of said annular member can compensate forlimited volume changes in said chambers and the attendant initialtendancy of the liquid to increase in pressure and flow from one chamberto the other through said choke opening, the axially facing surface areaof said annular member being substantially less than the axially facingsurface area of either of said chambers.
 2. An engine mount as claimedin claim 1 wherein said limited stroke of said annular member is suchthat the stroke volume of the annular member (the area of an axiallyfacing surface multiplied by the stroke distance) corresponds to thevolume change in said main chamber with an oscillation path of said endwalls relative to said support element of about 0.3 mm.
 3. An enginemount as claimed in claim 1 wherein said annular member is plate-likeand is loosely captured at its periphery in an inwardly open groovedefined in said partition, such that the flanks of the groove formstroke-limiting surfaces for said annular member.
 4. An engine mount asclaimed in claim 3 wherein one of said stroke-limiting surfaces of saidpartition includes fluid flow passages opening therein and which remainopen when said annular member is applied to said one stroke-limitingsurface.
 5. An engine mount as claimed in claim 1 wherein said annularmember has radially outwardly directed flanges extending over wallsurfaces of said partition to limit the stroke of said annular member.6. An engine mount as claimed in claim 1 wherein said annular memberforms an annular gap at its outer periphery with said partition.
 7. Anengine mount as claimed in claim 1 wherein said connecting meanscomprises a bolt extending between and connecting said end walls, saidbolt passing through said annular member with clearance such that saidclearance defines said choke opening.
 8. An engine mount as claimed inclaim 1 wherein at least the part of said annular member defining saidchoke opening is flexible such that an edge portion of said chokeopening undergoes changes with bending which change the flowcross-section and the flow coefficient of said choke opening.
 9. Anengine mount as claimed in claim 1 wherein said annular member isconnected with said partition by a rubber elastic flange.